Lead frame and its manufacturing method

ABSTRACT

A leadframe is plated with palladium only to a surface of a metal plate on which semiconductors elements are to be mounted and a surface of the metal plate to be placed on a substrate, and is not plated with palladium to lead portions, pad portions, other portions except for the surfaces to be plated and the side surface, of the leadframe, thereby, the amount of use of palladium is reduced to minimum and a cheap leadframe can be provided.

TECHNICAL FIELD

The present invention relates to a leadframe to be used forsemiconductor devices and manufacturing method of the same.

BACKGROUND ART

Conventionally, a leadframe is manufactured in such way that a patternof the leadframe is formed from a metal plate by etching or pressprocessing, then, after palladium plating is carried out to the wholesurface of it, semiconductor elements are mounted on the predeterminedposition, and then, after sealing with resin, cutting is carried out byusing a die etc. Finally, separate chips are produced. Such products arein practical use as electronic parts as IC chips.

In recent years, in a specification of the leadframe, the use of coatingby solder plating containing lead has ceased in consideration of theinfluence on environment, and palladium plating to the whole surface ofthe leadframe has been used. However, since palladium is an expensivemetal material, there is a problem of raising the product cost by usingpalladium plating to the whole surface.

Accordingly, the main object of the present invention is to provide acheaper leadframe by minimizing the amount of palladium used.

Other object of the present invention is to provide a manufacturingmethod of leadframe by which the fault of the leadframe is eliminated.

DISCLOSURE OF THE INVENTION

In order to attain the above-mentioned objects, the leadframe accordingto the present invention is characterized in that, in a leadframe whichis formed from a metal plate, palladium plating is partially carried outonly to necessary and minimum portions on which semiconductor elementsare to be mounted, portions to bond gold wires and portions to besoldered of a surface to be placed on a printed circuit board.

Besides, the leadframe according to the present invention ischaracterized in that, in a leadframe which is formed from a metalplate, palladium plating is carried out only to a surface on whichsemiconductor elements are to be mounted and a surface to be placed on aprinted circuit board, and that the palladium plating is not carried outto lead portions formed, pad portions, other portions except for thesurfaces to be plated and its side surface.

Besides, the leadframe according to the present invention ischaracterized in that, in a leadframe which is formed from a metalplate, palladium plating is carried out only to necessary and minimumportions of a surface on which semiconductor elements are to be mountedand a surface to be placed on a printed circuit board, the palladiumplating is not carried out to lead portions formed, pad portions, otherportions except for the portions of the surfaces to be plated and itsside surface.

According to the present invention, much cheaper leadframes can beprovided since the area to be plated with palladium can be minimized, incomparison with the conventional leadframe in which palladium plating iscarried out to the whole area.

Further, in the manufacturing method of a leadframe according to thepresent invention, a leadframe material is provided by forming a metalplate, and then, palladium plating is carried out only to portions whichare necessary and minimum for mounting of semiconductor elements of theleadframe material, and then, the plating is carried out to portions tobond gold wires and necessary and minimum portions to be soldered of asurface to be placed on a printed circuit board, of the leadframematerial.

Besides, in the manufacturing method of a leadframe according to thepresent invention, a leadframe material is provided by forming a metalplate, and then, palladium plating is carried out only to a surface ofthe leadframe material on which semiconductor elements are to be mountedand then, the plating is carried out only to a surface of the leadframematerial to be placed on a printed circuit board, while the plating isnot carried out to lead portions, pad portions, other portions exceptfor the surfaces to be plated and the side surface of the leadframematerial.

Besides, in the manufacturing method of a leadframe according to thepresent invention, a metal plate is prepared to form a leadframe, andthen, a resist layer is formed on the both sides of the metal plate. Andafter having made a mask (e.g. a mask, which is closely attached to thesurface of the resist layer, for exposing light, developing and plating)with a desired pattern of the leadframe on the surface of the resistlayer, the surface of the exposed metal plate is plated, wherein theplated layers containing at least palladium plated layer are formed andthen the mask is stripped, and a resist layer is again formed on thewhole both sides of the plate. Then, after exposing light by using themask with a predetermined pattern and developing are carried out, anetching mask is obtained. And then, the shape of lead portions, padportions and other portions are formed by etching.

Further, in the manufacturing method of a leadframe according to thepresent invention, a metal plate is provided to form a leadframe byforming the metal plate and then a resist layer is formed on the bothfront and back surfaces of the metal plate. And after having made a mask(e.g. a mask, which is closely attached to the surfaces of the resistlayer for exposing light, developing and plating) with a desired patternof the leadframe on the surface of the resist layer, the surface of theexposed metal plate is plated, wherein plated layers containing at leastpalladium plated layer is formed. Then, the resist layer is removed,etching of the metal plate is carried out by using the plated layer asan etching resist, wherein the etching is stopped before the portions ofthe metal plate which is necessary to be etched are penetrated by theetching. And then, the back surface of the metal plate is masked with atape, and the portion of the metal plate, which is necessary to beetched, is penetrated by carrying out etching again. Thus, the relationof positions of a number of lead portions etc. can be kept individuallyand independently by the tape.

Further, in the manufacturing method of a leadframe according to thepresent invention, a metal plate is provided to form a leadframe andthen a resist layer is formed on the both sides of the metal plate. Andafter having made a mask (e.g. a mask for carrying out etching which isclosely attached to the surface of the resist layer for exposing light,and then developing) with a desired pattern of the leadframe on thesurface of the resist layer, the exposed metal plate portion is removedby the etching and the pattern of leadframe is formed. Then, the bothfront and back surfaces of the leadframe are plated so as to form aplated layer containing at least palladium layer.

Further, in the manufacturing method of a leadframe according to thepresent invention, a metal plate is provided to form a leadframe and aresist layer is formed on the both front and back surfaces of the metalplate. And after making a mask (e.g. a mask for carrying out platingwhich is closely attached to the surface of the resist layer and towhich light is exposed and then developing is carried out) with adesired pattern of the leadframe on the surface of the resist layer, thesurface of the exposed metal plate is plated, thereby, plated layerscontaining at least palladium plated layer are formed. Then the resistlayer is removed and etching of the metal plate is carried out by usingthe plated layer as an etching resist. Thus, patterns of a number oflead portions, pad portions and others are formed.

According to the methods described above, the leadframe which is notonly cheaper but also does not cause such fault as missing of lead,breakage of resin etc., as seen in the conventional leadframe can beprovided since it is good enough to cut only the resin portion at thetime when the leadframe is cut into small chips by using the cutting ordicing device etc., after semiconductor elements are mounted on thepredetermined position on the leadframe and sealing is made by resinbecause the metal portions to be cut has already dissolved by theetching.

These and other objects as well as the features and advantages of thepresent invention will become apparent from the following the detaileddescription referred to the accompanying drawings.

BRIEF EXPLANATION OF DRAWINGS

FIG. 1A–1H is a flowchart illustrating an embodiment of manufacturing alead frame according to the present invention.

FIG. 2A–2H is a flowchart illustrating another embodiment ofmanufacturing a lead frame according to the present invention.

FIG. 3A–3H is a flowchart illustrating the other embodiment ofmanufacturing a lead frame according to the present invention.

FIG. 4A–4H is a flow chart illustrating further other embodiment ofmanufacturing a lead frame according to the present invention.

FIG. 5 is a schematic side view illustrating the positional relationbetween a lead frame manufactured by the method of the present inventionand a substrate as a printed circuit board.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1

FIG. 1 is a flowchart illustrating an embodiment of the manufacturingmethod of leadframe according to the present invention. In the FIG. 1, 1is a plate of copper or similar material for forming a leadframe. 2 is adry film mounted on the front and back surface of the metal plate 1. 3is a glass mask which is put on the dry film 2 placed on the surface ofthe metal plate 1, and which forms a leadframe pattern 3 a by using alight shielding agent. 4 is a glass mask which is put on the dry film 2placed on the back surface of the metal plate 1, and which forms aleadframe pattern 4 a on symmetrically opposite side to the leadframepattern 3 a with respect to the metal plate 1 by using the lightshielding agent. 5 and 6 are glass masks which form predeterminedshading patterns, and 7 are a plurality of etching liquid injectionnozzles which are disposed oppositely at both sides of the metal plate1.

Next, the manufacturing process of the leadframe will be explained inturn. First, as shown in FIG. 1A, the dry film 2 working as photoresistis placed on the whole front and back surfaces of the metal plate 1.Then, the glass masks 3 and 4 which have the leadframe patterns 3 a and4 a are put on the front and back surfaces at the state of positioningof the pattern. And such both surfaces are exposed by the ultra violetray through the glass masks 3 and 4.

After exposure, the glass masks 3 and 4 are removed and the metal plate1 with dry film is soaked into the developing solution for development.Thus only the portions of the dry film 2 exposed by the ultra violetray, i.e., portions which are necessary to be plated with palladium,such as portions to which gold wires are bonded and portions formounting thereon semiconductor elements are removed as shown in FIG. 1B.

Next, this is put into a plating tub, and as shown by partially enlargedscale in FIG. 1C, necessary plating of nickel (Ni), palladium (Pd) andgold (Au) etc. is carried out in turn for necessary portions. In thisway, the metal plate 1 with the plated layer 1 a of the cross-sectionalconfiguration as shown in FIG. 1D can be obtained by stripping the dryfilm 2.

The dry film 2 is again placed on the whole both front and back surfacesof the metal plate 1 with the plated layer 1 a which was obtained in theway as described above. Then, as shown in FIG. 1E, the glass masks 5 and6 on which the pattern is formed so as to shade only the plated portionsare put on the film 2 and the both sides are again exposed by the ultraviolet ray. Then, as explained in FIG. 1B, the development is carriedout, and the metal plate 1 with the plated layer 1 a of thecross-sectional configuration as shown in FIG. 1F is obtained.

As shown in FIG. 1G, etching is carried out by spraying etching liquidthrough the injection nozzles 7 on the both surfaces of the metal plate1 with plated layer 1 a. By this etching, the metal portions on whichplating is not carried out is dissolved and removed. Finally, bystripping the dry film 2, one frame of the leadframe which has thecross-sectional configuration as shown in FIG. 1H, that is, on whichplating was carried out only to the necessary minimum portion isobtained.

Each process shown in FIGS. 1A to 1H is carried out continuously byconveying a metal plate having the length including a plurality offrames on an appropriate conveyer and each frame of the leadframe iscompleted after being cut at the final stage of the process. As it isevident by the explanation above, consequently, palladium plating iscarried out only to necessary portions of the front and back surfaces ofeach leadframe.

Embodiment 2

FIG. 2 shows a flowchart illustrating another embodiment of themanufacturing method of leadframe according to the present invention. InFIG. 2, the same reference numerals in FIG. 1 are used to thesubstantially same components and portions, the explanation of thereference numerals are omitted. Since each process shown in FIGS. 2A,2B, 2C and 2D is the same as each process shown in FIGS. 1A, 1B, 1C and1D as it is clearly seen by comparison with FIG. 1, the explanation ofsuch process is omitted, with respect to each process shown after FIG.2E, the explanation will be made.

As shown in FIG. 2E, the etching is carried out by spraying the etchingliquid through the injection nozzles 7 to the both sides of the metalplate 1 with the plated layer 1 a. Such etching is carried out until themetal of the portion where the plating is not carried out becomesextremely thin in consequence of such metal having been almost dissolvedand removed.

After a tape 8 is attached, as shown in FIG. 2F, to the whole surface ofthe one side of the metal plate 1 with the plated layer 1 a which wasobtained in this way, the etching is again carried out by spraying theetching liquid through the injection nozzles 7 from the side to whichthe tape 8 is not attached as shown in FIG. 2G. Thus, the extremely thinmetal portions to which the plating is not carried out (unnecessaryportions, such as tie bars for connecting lead portions and hangingleads which are to be cut out after the assembling process) arecompletely dissolved and removed. In this case, the remained metalportions namely, such necessary portions as portions on whichsemiconductor elements are to be mounted, pad portions and lead portionswhere the plating has been carried out are certainly held withoutcollapsing relative positions by the tape 8, as shown in FIG. 2H.

Embodiment 3

FIG. 3 shows a flowchart illustrating still another embodiment of themanufacturing method of leadframe according to the present invention. InFIG. 3, the same reference numerals in FIG. 1 are used to thesubstantially same components and portions, the explanation of thosenumeral references is omitted. Since each process shown in FIGS. 3A and3B is the same as the process shown in FIGS. 1A and 1B as it is clearlyseen in comparison with FIG. 1, the explanation of such processes isomitted, with respect to each process shown after FIG. 3C, theexplanation will be made.

As shown in FIG. 3C, the etching is carried out by spraying the etchingliquid through the injection nozzles 7 on both sides of the metal plate1 on which the dry film 2 remains corresponding to the leadframepattern. Such etching is carried out until the metal plate 1 comes tohave penetrated holes as a consequence of dissolution and removal of themetal of portions on which the dry film 2 do not exist, as shown in FIG.3D. Thus the dry film 2 is stripped from the both surfaces of the metalplate 1 having the holes. In this way, the leadframe material with crosssectional configuration as shown in FIG. 3D is manufactured.

On the necessary portions on the front and back surfaces of theleadframe material (metal plate 1) obtained in this way, the nickel (Ni)plating, palladium (Pd) plating, and gold (Au) plating are carried out,respectively, as shown by an enlarged scale in FIG. 3E and then aleadframe is completed. That is to say, as shown in FIG. 3F, at first,the nickel (Ni) plating is carried out to the whole surface of the frontand back surfaces of the leadframe as a ground layer, and then as shownin FIG. 3G below, the palladium (Pd) plating is carried out only to thenecessary minimum portions for semiconductor mounting portions, portionsto bond gold wires and portions to be soldered of the surface to be on aprinted circuit board. Finally, as shown in FIG. 3H, the gold (Au)plating is carried out to the both sides of the front and the backsurfaces of the leadframe and then a leadframe is completed. Thus,according to the present invention, the amount of the expensivepalladium used can be at a minimum, and the finished product of aleadframe is much cheaper as compared with the conventional leadframe.

Embodiment 4

FIG. 4 shows a flowchart of still another embodiment of themanufacturing method of leadframe according to the present invention.The same reference numerals used in FIG. 1 are given to thesubstantially same components and portions and the explanation aboutthem is omitted. The explanation of FIGS. 4A to 4D is omitted since eachprocess is the same as those of FIGS. 1A to 1D as it is evident bycomparison with FIGS. 1A to 1D. The processes shown after FIG. 4E willbe explained.

This embodiment differs from the first embodiment in such point that theproduct is manufactured by the etching, that is, by spraying the etchingliquid through the injection nozzles 7 on both sides of the metal plateobtained in FIG. 4 D on which the plating was completed without carryingout the second light exposure and the development. According to thisembodiment, the product can be provided much cheaper.

As explained above, according to the present invention, the leadframewhich is not only much cheaper but also does not cause fault such asmissing of lead and breakage of resin in comparison with the product bythe conventional method can be provided.

1. A leadframe formed from a metal plate, comprising: a first surfacefor mounting thereon a semiconductor element, a second surface to beplaced on a printed circuit board, and shaped lead portions, whereinnickel, palladium and gold are plated in turn only to said first andsecond surfaces, while said shaped lead portions, non-mounted portionsincluding pad portions, and said faces of said leadframe are free fromplating.
 2. A leadframe formed from a metal plate, comprising: a firstsurface for mounting thereon a semiconductor element, a second surfaceto be placed on a printed circuit board, and shaped lead portions,wherein nickel, palladium only and gold are plated in turn only to anecessary and minimum part of said first and second portions, while saidshape lead portions, non-mounted portions including pad portions, andside faces of said leadframe are free from plating.